Dummy bar head for continuous casting and method of using same

ABSTRACT

In continuously casting steel wherein the bottom end of an openended chill mold is closed for the start of casting by the head of a dummy bar, the upper end of the dummy bar head which is received within the mold is undercut on one side to form with an adjacent wall of the mold a cavity into which molten steel poured into the mold is received and solidifies. The undercut side of the head has a projection to extend into the cavity and toward said first wall of the mold. The face of the upper end of the head in back of the projection has at least a part of its surface bearing against the mold wall which is opposite said first mold wall, when the head is in the mold. The projection and the cavity are shaped to enable the upper end of the head to be separated from the steel that has solidified in contact therewith in the mold, after the head and said solidified steel are withdrawn from the mold, by transverse circular movement of the lower end of the head away from the portion of the steel that solidified in the cavity.

United States Patent Appl. No. Filed Patented Assignees Priorities DUMMYBAR HEAD lFOR CONTINUOUS CASTING AND METHOD OF USING SAME 15 Claims, 6Drawing Figs.

[1.8. CI 1164/82, [64/274 llnt. Cl B22d 11/08 Field of Search 164/82,274, 282, 283

Primary ExaminerR. Spencer Annear Aimrney-Sandoe, Hopgood & CalimafdeABSTRACT: In continuously casting steel wherein the bottom end of anopen-ended chill mold is closed for the start of casting by the head ofadummy bar, the upper end of the dummy bar head which is received withinthe mold is undercut on one side to form with an adjacent wall of themold a cavity into which molten steel poured into the mold is receivedand solidifies. The undercut side of the head has a projection to extendinto the cavity and toward said first wall of the mold. The face of theupper end of the head in back of the projection has at least a part ofits surface bearing against the mold wall which is opposite said firstmold wall, when the head is in the mold. The projection and the cavityare shaped to enable the upper end of the head to be separated from thesteel that has solidified in contact therewith in the mold, after thehead and said solidified steel are withdrawn from the mold, bytransverse circular movement of the lower end of the head away from theportion of the steel that solidified in the cavity.

DUMMY MAIN HEAD FOR CONTINUOUS CASTING AND METHOD OF USING SAMllE Thepresent invention relates to a method and apparatus for continuouslycasting steel, wherein the bottom end of an open-ended chill mold isclosed by a dummy bar head before pouring begins, the dummy bar headhaving a configuration so that molten steel poured into the mold bysolidifying in the mold forms a strand and creates a connection betweenthe strand and the dummy bar head, which connection permits the strandto be withdrawn, and, after withdrawal and further cooling of thestrand, is quickly and easily broken for detaching the dummy bar headfrom the strand.

For starting a continuous casting a dummy bar connected to a dummy barhead is required. When pouring begins the dummy bar head closes the openbottom end of the mold and must later be detached from the strand.

PRIOR ART A known method of connecting the head to the dummy bar is bymeans of a hook-shaped coupling and to uncouple the head from the dummybar by relative displacement laterally with respect to the longitudinalcasting axis. One drawback of this method is the rigid connection ofpart of the dummy bar head to the strand by coupling elements whichremain embedded in the strand after separation. For the purpose ofseparation the dummy bar head must first be cut off from the end of thestrand and after cooling the coupling elements must be removed from thedummy bar head. Consequently, these operations cannot be carried outduring casting. This involves loss of time because the dummy bar headcannot be immediately reintroduced into the end of the mold to permitpouring of the next casting to commence. If no time is to be lost,several heads for castings of different cross sections must be keptavailable.

It has already been proposed to insert coupling elements such as railsinto the head, said rails forming the coupling of the dummy bar head tothe steel in the mold for withdrawal of the cast strand. These couplingelements which remain embedded in the end of the strand are separatedfrom the dummy bar head by application of lateral thrust. In thisprocedure time and material are wasted because new coupling elementsmust be inserted into the head for each new casting and the elementsthat have been embedded in the casting are lost.

Recurrent difficulties are experienced, principally because the caststeel welds not only to the coupling elements but also to the head andtherefore complicates and delays the separation. Additional difficultiesarise because forces due to shrinkage stress act on the rails and causethem to warp in their sockets, so that special devices are needed foreffecting separation. Furthermore, these rails interfere with thenatural shrinkage and cause extended cracks to appear at the leading endof the casting, which cause considerable waste.

OBJECT OF THE INVENTION It is the object of the present invention toprovide a method, and apparatus for performing the method, ofsatisfactorily withdrawing the cast strand, and of detaching the end ofthe strand from the head at the end of the dummy bar while castingcontinues, in a relatively simple way and in a manner that requires noadditional coupling elements.

BRIEF DESCRIPTION OF THE INVENTION According to the invention this isachieved by partly embedding the head in the steel in a configurationpermitting the head to perform a rotary and/or tilting motion, thoughcreating an interfitting coupling connection for withdrawing thecasting. The head is subsequently detached by rotating and/or tilting itin a manner deflecting its longitudinal axis out of alignment with thelongitudinal axis of the casting and then, after complete separation,removing the head from the path of the casting.

In order to prevent unwanted transverse displacement of the headrelative to the casting due to components of thrust generated betweencoacting geometries during withdrawal, another feature of the proposedmethod consists in providing a component of force which counteracts anysuch transverse displacement.

The proposed apparatus for performing the method is characterized inthat the upper part of the head is formed at least in its central regionwith a portion projecting towards the opposite wall of the mold, saidprojection having surfaces geometrically designed to be separable fromthe solidified casting by a rotary and/or tilting motion of the headwhereas at least the face of said upper part of the head on the back ofsaid projection at least partly bears against the cooperating mold walland the upper face of the bottom part of the head closes the remainderof the open end of the mold.

In order to facilitate the separation of the head from the casting theprojection according to the invention may be of semicylindrical shape;as a variation the cylindrical projection may have a flat face on theside facing the opposite mold wall. The projection provides an edge orfulcrum about which the head can tilt and thereby effect a rapid andclean separation.

As is well known, the weight of the casting may apply a downward thrustto the head. Owing to the particular configuration of the projection,this thrust could displace the head transversely with respect to thecasting and cause premature separation. However, this is prevented witha dummy bar head of this invention by having the upper face of thebottom part of the head inclined at a positive angle to a plane normalto the casting axis.

To provide a satisfactory seal at the lateral walls of the mold, thelateral walls of the upper part of the head are flush against the moldwalls. Preferably the lateral parts of the head may be trapezium shaped.

The force required for the withdrawal of the casting could likewisecause transverse displacement and premature disengagement. In order toprevent this from occurring it is further proposed that the faces of theupper part of the dummy bar head facing the open end of the mold couldalso be inclined at a positive angle to a plane normal to the castingaxis. Moreover, it is proposed that the angle formed by a plane tangentto the surface of the projection at its bottom edge with a plane normalto the casting axis could be less than the positive angle of theaforementioned faces. Alternatively, the angle of the upper face of thebottom part of the head could be equal to or smaller than the angle atthe bottom edge of the projecting surface.

Furthermore, in order to ensure that the initiation of a tilting motionwill cause a rapid separation of the head from the casting, it ispreferred to place the edge about which the head will tilt in the regionwhere the surface on the back of the projection intersects a flatsurface of the top of the projection.

THE DRAWINGS;

These and other features of the invention will now be more particularlydescribed with reference to embodiments shown in the drawings in which:

FIG. I is a cross-sectional view of a dummy bar head in accordance withthis invention inserted into the open end of a mold,

FIG. 2 is an elevation of the dummy bar head of FIG. ll,

FIG. 3 is a cross section ofone form ofdummy bar head embodying theinvention and of the solidified steel in which it has been embedded,showing the head in the process of being detached by tilting,

FIG. 41 is a cross section of another form of dummy bar head and of thesteel in which it has been embedded, showing the head in the course ofbeing detached by a rotary motion,

FIG. 5 is another embodiment of a dummy bar head which in configurationresembles a catch, and

FIG. 6 is a partial elevation of the embodiment shown in FIG. 5.

DETAILED DESCRIPTION With reference to FIG. 1, a cooled open-ended moldl is shown with a dummy bar head 2 inserted therein, the lower part 3 ofthe head plugging the open bottom end of the mold 1. This lower part 3of the head 2 is attached by hinge means indicated at 49 to a dummy bar(not shown).

The upper part 4 of the head 2, which in this embodiment is integrallyformed with the bottom part 3, is provided in its center region with acavity including a substantially semicylindrical projection 5 whichextends towards the opposite wall 6 of the mold. As an alternative, theupper part 4 of the head might be detachably connected to the lower part3 to facilitate a replacement of the upper part which is exposed togreater wear. The bottom part 3 is formed with recesses 24 and 25 whichinterfit with the end of the dummy bar (not shown).

The semicylindrical projection 5 which faces the opposite wall 6 of themold has a smooth curved surface 7 terminating along a line 8 at thebottom. However, this projecting portion 5 might also be bounded bydifferently shaped arched and/or flat faces. At the upper portion ofprojection 5 the surface 7 merges into a flat face 9 which forms afulcrum at 27. The described form of construction therefore provides afulcrum 27 about which the dummy bar head can tilt at the line ofintersection between the face 9 and the side 12 of the head at the backof the projection 5. A separation of the head from the steel in which itis embedded is thereby substantially facilitated.

In the embodiment shown in H0. 2 the projection 5 is in the centralportion of the head and ends at the side faces 31 and 32. The projection5 could, however, be made to extend all the way across the head to theadjacent walls of the mold.

Molten steel is poured into the mold 1 from a pouring vessel (not shown)and the dummy bar head 2 is embedded therein in a manner permitting thehead to be disconnected subsequently from the solidified strand by beingrotated or tilted relative to the strand. Since the back 12 of theprojection, and preferably also the side faces l4, (FIG. 2) of the upperpart 3 of the head 2 bear against the mold walls, it is difficult forthe steel to enter the interfaces. Such entry ofsteel may be even moreeffectively prevented by the interposition of sealing means, such asasbestos cords, and to facilitate placement of asbestos cords betweenthe mold walls and the adjacent faces of the head the correspondingedges of the head are bevelled as indicated at 26.

By suitably designing the dimensions of the head, sufficient heat isimmediately abstracted from the steel poured into the cavity between themold wall 6 and the projection 5 to cause the steel to solidify withoutwelding to the head. At the same time a geometrically interfittingcoupling connection is formed between the head and the casting formed inthe' mold so that the casting can be withdrawn with the aid of the head.As soon as this coupling has been established, the withdrawal of thecasting from the mold is initiated by a withdrawing unit (not shown).After leaving the mold the casting is further cooled in a secondarycooling zone and eventually discharged completely from the castingapparatus.

For detaching the head from the casting the head is first slightlyturned and then tilted about the fulcrum edge 27 so that its axis isdeflected out of alignment with the longitudinal axis 11 of the castingand then completely removed from the path of the casting.

When castings are produced in a continuous casting plant equipped withan arcuate guideway for the withdrawal of the casting therethrough, thedummy bar (not shown) which may consist of an articulated chain, forexample passes through a withdrawing unit and is pulled onto a tiltabletable which is located above the exit for the casting. The head can thenbe detached from the casting by the tilting of the table. Thisarrangement permits the head to be detached in an extremely simple way.However, other methods of detaching the head can be devised.

One major advantage afforded by the proposed method is that the head canremain on the dummy bar and is thus immediately ready for reuse forstarting a successive casting run. The resultant saving in time isparticularly significant when new charges are to be poured in continuoussuccession.

As already described, the face 12 of the head on the back of theprojection 5 is adapted to be in flush contact with the wall 10 of themold. The two side faces l4, 15 of the head, as shown in FIG. 2, maylikewise bear flush against the adjacent walls of the mold.Alternatively, these faces l2, l4 and 15 could be arranged to makecontact with the mold wall only along a short part of their length oreven only along one edge, the remainder being at a certain possiblyvarying distance from the adjacent mold wall.

The upper part 4 of the head may have top end faces 16 and 17 which, asshown, may be inclined at a positive angle 19 to a plane 18 nonnal tothe longitudinal casting axis 11. This positive angle 19 should begreater than an angle 20 between a plane 21 tangent to the surface ofthe projection 5 at its bottom edge 8 and the associated normal plane18'. As subsequently described, the lower part of the face of theprojection 5 may also be flat, in which case the angle 20 is the anglebetween this latter flat face and the plane 18'. This arrangement ofangles counteracts the component of force which is generated by thecurved geometry of the projection 5 in the adjacent metal of the castingand which tends undesirably to displace the head transversely withrespect to the casting.

The upper face 22 of the bottom part 3 of the head-a face which may bereferred to as the undercut face is likewise set at a positive angle 23to a plane 18" normal to the casting axis 11. This angle 23, which maybe smaller than or equal to the angle 20, likewise prevents the headfrom being undesirably thrust out of coupling engagement with thecasting and of being prematurely detached therefrom.

Thus, as just described, and as shown in the drawings, each of theangles 23 and 19 operate to prevent premature transverse displacement ofthe head. Experience has shown, however, that the positive angle 23 ofthe undercutting face 22 is usually enough to prevent any unwanteddisplacement of the head relative to the casting so that the degree anddirection of the angle 19 is not critical in most cases, and may be anegative angle. To facilitate sealing at the bevelled edges 26 theprojection 5 may be shortened, the positive angle 23, and also thepositive angle 20, may be enlarged, and the angle 19 may be a negativeangle, even to the extent that the positive angle 23 and the negativeangle 19 are inclined so that the bevelled edges 26 of the end faces 16,I7 meet the bevelled edge 26 of the undercut face 22. Thus the sealingedge of the head inclines little, and it is easier to place scrap on thehead for accelerating the cooling of the molten steel in the mold.

Unwanted displacement of the head relative to the casting may also beresisted by the provision of appropriate guide means, such as rollers,until such time as the head and the leading end of the casting reach thepoint where they are intended to be uncoupled.

FIG. 3 shows another embodiment of the invention in which the projection5 has an additional flat contact face 7 merging into a curved face incasting direction. This remaining curved face could likewise be replacedby a flat face. FIG. 3 also shows this head 2 in the position itoccupies when it is being tilted or tipped out of engagement, thetipping motion being about a fulcrum edge 27 which is in the regionwhere the face 12 at the back of the projection 5 intersects the upperflat face 9. The position of the fulcrum edge 27 is substantiallydetermined by the position and shape of the contact face 7' which mustbe so disposed in relation to the fulcrum edge 27 that a tilting motionabout this edge will disengage the head without jamming the head bycontact between the tilted head and the surrounding solidified steel ofthe casting.

FIG. 4 is yet another embodiment of the head in which the projection 5has a semicylindrical contact face 7" which thus has the generalconfiguration of one-half of a roller having its axis at 30. However,curved faces of other configurations would also form suitable contactfaces. A semicylindrical face as shown at 7" permits the head to bedetached by first rotating it in the enveloping steel about the axis 30and then pulling it off the end of the casting.

FIG. shows another embodiment wherein the upper part d of a head 2which, in shape, resembles a catch so that the casting 28 solidifies toform a nose in the undercut recessed portion of the upper part 4) of thehead. As shown, the undercut faces 4m and d3 of the recess and thesurface Ml at the bottom of the recess have molded the faces d0, All anddid of the nose of the casting. The face d6 of the casting has beenmolded by the wall of the cooled mold.

in the drawing the head 2 is shown in a position in which it is in theprocess of being detached. The upward extension of the head contains asystem axis 53 about which the rotary or tipping motion of the headtakes place. The upper end face 60 of part 4) of the head is curvedrelative to this system axis 53 and causes a recessed complementarymating face to be molded into the adjacent end portion of the casting23. During the tilting motion of part d these two complementary faces donot at first separate, but slide relatively across each other.

On the left of the system axis 53 is a center 5d about which the faceall of the nose curves at a radial distance fl, and on the right of thesystem axis 53 is a second center 55 about which the other face 4M) ofthe casting nose curves at a radial distance 5t). A tilting motion ofthe head about the system axis 53 causes the center 55 to move to thepoint marked 57, whereas the center 5d moves to 56, so that the undercutfaces 42 and 43 are situated on circles, having radii 6i) and $1, aboutthe points 57 and 56. It will be seen that a small angle of tilt opensup a relatively wide clearance gap between the faces 41 and d3 as wellas between MB and 42, and that an increase in the angle of tilt leadsrapidly to the creation of a wide gap between the head and thecorresponding faces of the casting. At the same time the surfaces M andd5 will of course move away from each other. The tilting motion fordisconnecting the head does not proceed to completion about the systemaxis 53, but in its final stages is about the fulcrum edge 27.

The edge between the curved face 60 of the head and its baclt face 12,which bears against the sidewall of the mold, is preferably chamfered toform a bevel 26. A sealing material is rammed into the angle between thebevel face 26 and the sidewall of the mold, and this sealing materialwill usually remain adhering to the casting 28 in the form ofa narrowfillet 68.

FIG. 6 is a partial elevation of a dummy bar head having a shaperesembling a catch for use in a casting plant for continuously castingslabs. Adjacent its end faces M (and 15, not shown) the head has atrapezium-shaped configuration 59 which facilitates sealing.Transversely of the longitudinal axis of the casting, the recess, whichis to be filled with steel, tapers, so that the side face 46, (FIG. ofthe casting is widest and the casting narrows towards the projection andthus facilitates the separation of the head from the casting. The lowerpart 3 of the head 2 is provided with the coupling pin 52 which connectsthe head to the rest of the dummy bar (not shown) and which permits thehead to be pulled out of alignment with the casting by the dummy bar soas to perform the desired tilting motion of the head.

What is claimed is:

l. A method of continuously casting steel comprising closing the bottomend of an open end chill mold by a dummy bar head before pouring begins,then pouring molten steel into the mold, cooling the molten steel in themold, which by solidifying in the mold adjacent the dummy bar head andthe mold walls causes a direct interfitting coupling connection to beformed between the casting and the dummy bar head, thereby permittingthe casting to be withdrawn, withdrawing the dummy bar head and castingfrom the mold, and, after withdrawal and further cooling of the casting,detaching the dummy bar head therefrom, said method being characterizedin that the dummy bar head which comprises a hook-shaped projection atits upper end which is partly embedded in the solidified steel of thecasting in a configuration permitting the head to perform a tiltingmotion with respect to the casting is tilted with respect to the castingin a manner deflecting its longitudinal axis out of alignment with thelongitudinal axis of the casting to separate said dummy bar head fromthe casting, and, after complete separation, removing the dummy bar headfrom the path of the casting.

2. The method of claim ll, characterized in that the steel whichsolidifies above the dummy bar head and between the dummy bar head andthe mold wall counteracts any unwanted transverse displacement of thedummy bar head in relation to the casting caused by components of thrustgenerated between coacting geometries during withdrawal.

3. A dummy bar head for use in apparatus for the continuous casting ofsteel wherein the bottom end of an open-ended chill mold is closed forthe start of casting by a dummy bar head placed therein before steel ispoured into the mold, said head having its upper end undercut at oneside to form with a first adjacent wall (6) of the mold a cavity intowhich molten steel poured into the mold is received and solidifies, saidundercut side of the head having a projection (5) extending into saidcavity and toward said first wall of the mold when the head is in themold, the face (E2) of the upper end of the head in back of theprojection having at least a part of its surface bearing against themold wall (10) which is opposite said first wall when the head is in themold, the surfaces of said projection being arched and terminating in atransverse fulcrum edge to enable the upper end of the head to beseparated from steel that has solidified in contact therewith in themold, after the head and said solidified steel are withdrawn from themold, by tilting movement of the lower end of the head away from theportion of the steel that has solidified in the cavity.

4). The dummy bar head of claim 3, characterized in that the projection(5) is semicylindrical.

5. The dummy bar head of claim 3, characterized in that the projection(5) has at least one flat face (9,7') facing the opposite mold wall (6).

I 6. The dummy bar head of claim 3, characterized in that the lateralfaces (M, 15) of the upper part (4) of the dummy bar head bear againstthe walls of the mold.

7. The dummy bar head of claim 6, characterized in that the inside faces(59) of the lateral parts of the dummy bar head are inclined toward thelongitudinal casting axis 1 l) to form a cavity which tapers in thecasting withdrawal direction.

h. The dummy bar head of claim 3, characterized in that a fulcrum edge(27) is provided in the region where the said face (112) in the backofthe projection (5) intersects the upper edge of the projection.

9. The dummy bar head of claim 3, characterized in that the upper face(22) of the bottom of the cavity in the dummy bar head is inclinedupwardly toward said adjacent first wall (6) at an acute positive angle(23) to a plane (11%") normal to the longitudinal casting axis (111).

110. The dummy bar head of claim 9, characterized in that said acutepositive angle (23) is equal to or smaller than the positive angle (20)between a plane (2i) tangent to the surface of the projection (5) at itsbottom edge (3) and a plane (1%) normal to the longitudinal casting axis(Ill) and intersecting said bottom edge (8).

11. The dummy bar head of claim 31, characterized in that the top faces(l6, l7) of the dummy bar head are inclined upwardly toward saidadjacent first wall (6) at an acute positive angle (19) to a plane(llfi) normal to the longitudinal casting axis l l 112. The dummy barhead of claim ll, characterized in that said acute positive angle (i9)is greater than said acute positive angle (20) between a plane (21)tangent to the surface of the projection (5) at its bottom edge (h) anda plane (18') normal to the longitudinal casting axis (ill) andintersecting said bottom edge (h).

13. The dummy bar head of claim 3, characterized in that the surface(60) of the upper portion of the projection (5) fac ing said first wall(6) of the mold is curved on a first radius about a first center (53)located in the upper end portion of the head, that the surface (d3) ofthe lower portion of the projection facing said first wall (6)"is curvedon a second radius, longer than the first, about a second center (54)which is spaced from the first center at the side thereof away from thesurface of the projection and close to a line transversely through thefirst center from the surface of the projection to said face of the headin back of the projection, and in that the surface (42) of the upperface (22) of the bottom of said cavity is curved on a third radius,longer than the second, about a third center (55) which is spaced fromthe first center at the side thereof toward the surface of theprojection and close to said transverse line through the first center.

14. The dummy bar head of claim 13, characterized in that i i t IUIOM(H77

1. A method of continuously casting steel comprising closing the bottomend of an open end chill mold by a dummy bar head before pouring begins,then pouring molten steel into the mold, cooling the molten steel in themold, which by solidifying in the mold adjacent the dummy bar head andthe mold walls causes a direct interfitting coupling connection to beformed between the casting and the dummy bar head, thereby permittingthe casting to be withdrawn, withdrawing the dummy bar head and castingfrom the mold, and, after withdrawal and further cooling of the casting,detaching the dummy bar head therefrom, said method being characterizedin that the dummy bar head which comprises a hookshaped projection atits upper end which is partly embedded in the solidified steel of thecasting in a configuration permitting the head to perform a tiltingmotion with respect to the casting is tilted with respect to the castingin a manner deflecting its longitudinal axis out of alignment with thelongitudinal axis of the casting to separate said dummy bar head fromthe casting, and, after complete separation, removing the dummy bar headfrom the path of the casting.
 2. The method of claim 1, characterized inthat the steel which solidifies above the dummy bar head and between thedummy bar head and the mold wall counteracts any unwanted transversedisplacement of the dummy bar head in relation to the casting caused bycomponents of thrust generated between coacting geometries duringwithdrawal.
 3. A dummy bar head for use in apparatus for the continuouscasting of steel wherein the bottom end of an open-ended chill mold isclosed for the start of casting by a dummy bar head placed thereinbefore steel is poured into the mold, said head having its upper endundercut at one side to form with a first adjacent wall (6) of the molda cavity into which molten steel poured into the mold is received andsolidifies, said undercut side of the head having a projection (5)extending into said cavity and toward said first wall of the mold whenthe head is in the mold, the face (12) of the upper end of the head inback of the projection having at least a part of its surface bearingagainst the mold wall (10) which is opposite said first wall when thehead is in the mold, the surfaces of said projection being arched andterminating in a transverse fulcrum edge to enable the upper end of thehead to be separated from steel that has solidified in contact therewithin the mold, after the head and saId solidified steel are withdrawn fromthe mold, by tilting movement of the lower end of the head away from theportion of the steel that has solidified in the cavity.
 4. The dummy barhead of claim 3, characterized in that the projection (5) issemicylindrical.
 5. The dummy bar head of claim 3, characterized in thatthe projection (5) has at least one flat face (9,7'') facing theopposite mold wall (6).
 6. The dummy bar head of claim 3, characterizedin that the lateral faces (14, 15) of the upper part (4) of the dummybar head bear against the walls of the mold.
 7. The dummy bar head ofclaim 6, characterized in that the inside faces (59) of the lateralparts of the dummy bar head are inclined toward the longitudinal castingaxis (11) to form a cavity which tapers in the casting withdrawaldirection.
 8. The dummy bar head of claim 3, characterized in that afulcrum edge (27) is provided in the region where the said face (12) inthe back of the projection (5) intersects the upper edge of theprojection.
 9. The dummy bar head of claim 3, characterized in that theupper face (22) of the bottom of the cavity in the dummy bar head isinclined upwardly toward said adjacent first wall (6) at an acutepositive angle (23) to a plane (18'''') normal to the longitudinalcasting axis (11).
 10. The dummy bar head of claim 9, characterized inthat said acute positive angle (23) is equal to or smaller than thepositive angle (20) between a plane (21) tangent to the surface of theprojection (5) at its bottom edge (8) and a plane (18'') normal to thelongitudinal casting axis (11) and intersecting said bottom edge (8).11. The dummy bar head of claim 3, characterized in that the top faces(16, 17) of the dummy bar head are inclined upwardly toward saidadjacent first wall (6) at an acute positive angle (19) to a plane (18)normal to the longitudinal casting axis (11).
 12. The dummy bar head ofclaim 11, characterized in that said acute positive angle (19) isgreater than said acute positive angle (20) between a plane (21) tangentto the surface of the projection (5) at its bottom edge (8) and a plane(18'') normal to the longitudinal casting axis (11) and intersectingsaid bottom edge (8).
 13. The dummy bar head of claim 3, characterizedin that the surface (60) of the upper portion of the projection (5)facing said first wall (6) of the mold is curved on a first radius abouta first center (53) located in the upper end portion of the head, thatthe surface (43) of the lower portion of the projection facing saidfirst wall (6) is curved on a second radius, longer than the first,about a second center (54) which is spaced from the first center at theside thereof away from the surface of the projection and close to a linetransversely through the first center from the surface of the projectionto said face of the head in back of the projection, and in that thesurface (42) of the upper face (22) of the bottom of said cavity iscurved on a third radius, longer than the second, about a third center(55) which is spaced from the first center at the side thereof towardthe surface of the projection and close to said transverse line throughthe first center.
 14. The dummy bar head of claim 13, characterized inthat the second and third centers (54, 55) are approximately equidistantfrom the first center (53).
 15. The dummy bar head of claim 13,characterized in that the second center (54) of the surface (43) of thelower portion of the projection facing said first wall (6) of the moldis above said transverse line.